In general, a particle beam therapy system is provided with a beam generation apparatus that generates a charged particle beam; an accelerator that is connected with the beam generation apparatus and accelerates a generated charged particle beam; a beam transport system that transports a charged particle beam that is accelerated by the accelerator so as to gain predetermined energy and then emitted; and a particle beam irradiation system, disposed at the downstream side of the beam transport system, for irradiating an irradiation subject with a charged particle beam. Particle beam irradiation systems are roughly divided into a broad irradiation method in which a charged particle beam is enlarged in a scattering manner by a scatterer, and the shape of the enlarged charged particle beam is made to coincide with the shape of an irradiation subject in order to form an irradiation field; and a scanning irradiation method (the spot-scanning method, the raster-scanning method, and the like) in which an irradiation field is formed by performing scanning with a thin, pencil-like beam in such a way that the scanning area coincides with the shape of an irradiation subject.
In the broad irradiation method, an irradiation field that coincides with the shape of a diseased site is formed by use of a collimator or a bolus. The broad irradiation method is a most universally utilized and superior irradiation method where an irradiation field that coincides with the shape of a diseased site is formed so as to prevent unnecessary irradiation onto a normal tissue. However, it is required to create a bolus for each patient or to change the shape of a collimator in accordance with a diseased site.
In contrast, the scanning irradiation method is a high-flexibility irradiation method where, for example, neither collimator nor bolus is required. However, because these components for preventing irradiation onto not a diseased site but a normal tissue are not utilized, there is required a positional accuracy of beam irradiation that is the same as or higher than that of the broad irradiation method.
Patent Document 1 discloses an invention, stated below, that has an objective of providing a particle beam therapy system capable of accurately irradiating a diseased site. In the invention disclosed in Patent Document 1, there are stored, in a memory device, the amount of charged particle beams scanned by a scanning apparatus and the position of a charged particle beam detected by a beam position detector while the charged particle beam is emitted; then, by utilizing the stored scanning amount and the beam position, the scanning amount of the beam scanning apparatus is set by a control apparatus, in accordance with the beam position based on information about a treatment plan. The relationship between the scanning amount and the beam position, which is obtained by actually performing irradiation, is stored in the memory device; therefore, accurate irradiation onto a diseased site can be expected.